1. Field of the Invention
The present invention relates to an electrode composition for plasma display panels (PDP), and more particularly to improvements in the conductive components included in black bus electrodes.
2. Technical Background
In PDP, black components are included in the bus electrodes of the front panel to improve the contrast. Single- and double-layered types of bus electrodes are known in the art. A black component is included along with a conductive component such as silver in the single-layered type. In the double-layered type, a white electrode containing a conductive component such as silver is stacked with a black electrode (black bus electrode) containing the black component.
Ruthenium oxide, ruthenium compounds (e.g. Japanese Patent JP3779297), Co3O4 (JP3854753), Cr—Cu—Co (US patent publication 2006-0216529), lanthanum compounds (JP3548146), and CuO—Cr2O3—Mn2O3 (JP3479463) are known as black components.
Black components with a high degree of blackness are preferred for improving the contrast in PDP. Blackness is usually assessed as the L value in PDP. On the other hand, low contact resistance is also an element that is considered important as well as blackness. Because black components have higher resistance than conductive metals such as silver or copper, there has long been a need to find a way to combine the mutually conflicting factors of lower contact resistance and higher blackness to improve contrast.
Ruthenium oxides and ruthenium compounds have a high degree of blackness as the black component and are also conductive, and have conventionally been preferred for use to obtain high blackness and low contact resistance in PDP. However, the development of less expensive materials is needed in order to make the price of PDP more competitive.
Adding a highly conductive, inexpensive metal, for example copper, nickel or palladium, to the black bus electrode and minimizing the amount of the expensive black component is one method of reducing material costs. However, copper characteristically tends to oxidize, and must therefore be sintered in a reducing atmosphere. Also, nickel has relatively low conductivity. Palladium releases oxygen, particularly during reduction, as a result of the redox reaction during the sintering process, and thus results in a considerable loss of the bus electrode properties.
Ag is a desirable material that is highly conductive and inexpensive, but the Ag atoms are diffused into glass during the sintering process, and a resulting problem is yellowing of the black stripes that are formed (cf. JP3779297). Because of the yellowing, the addition of Ag to the black bus electrodes formed on the front panel side results in a loss of PDP contrast.
JP2006-86123 has disclosed a technique relating to conductive powder used in PDP electrodes, where a powder comprising silver or gold coated with copper, nickel, aluminum, tungsten, or molybdenum is used as a conductive powder in PDP electrodes or green sheets.
JP2002-299832 also discloses a technique in which Pd-containing Ag prepared by co-precipitation is used to form electrodes on a glass substrate. It is claimed that this results in better adhesion between the glass substrate and the electrodes, low resistance, and better migration resistance. JP2002-299832 is characterized by the use of Ag and Pd co-precipitated powder instead of a mixture of Ag powder and Pd powder or Ag—Pd alloy (Paragraph 0011). PDP electrodes were disclosed as the electrode application. Although the language is not explicit, the electrodes of JP2002-299832 are formed on a glass substrate, and as a result, it may be concluded that address electrodes formed on the rear panel of a PDP are intended in light of the fact that adhesion with glass is claimed (such as Paragraph 0014) as well as the fact that a substrate on which a paste composition (Paragraphs 0059 and 0062), electrodes, barrier walls, and a fluorescent material have been formed is sealed with a front panel (Paragraph 0075).
In order to improve PDP properties and avoid some of the undesirable results mentioned above, it is desirable to provide a black bus electrode that has a high degree of blackness and low contact resistance.